It is often desirable to maintain different areas or rooms in a building at different temperatures. For example, rooms used extensively typically require a higher level of heating or cooling than rooms which are less used. Some rooms in a centrally heated building may be heated by auxiliary heating means such as a wood stove. This creates a requirement for a central heating system that can deliver heat energy to rooms on a room-by-room basis. Present systems for heating or cooling selected areas typically deliver a working fluid to a zone of areas through a single circulating loop. Room-by-room temperature control within a single circulating loop is typically established by the use of by-pass piping and thermostatically controlled valves connected to the system at each room.
The complexity, large number of parts, and time required to install room-by-room temperature control systems leads to a high system cost. Modification of conventionally zoned single circulating loop systems to provide room-by-room temperature control requires professional plumbing and electrical skills.